The present invention relates generally to a prismatic battery, and more particularly to a prismatic battery comprising a terminal structure with enhanced airtightness and high volumetric efficiency.
Many varied types of batteries are used as power sources for miniature electronic equipment. Not only cylindrical batteries but also prismatic batteries able to make effective use of small spaces are widely used to make accommodations to the miniaturization of equipment. Referring typically to one example of a closed type prismatic battery shown in FIG. 7, a power-generating element is inserted into a metallic battery can 71, and the outer can is used as one electrode or a negative electrode terminal. A metal sheet 74 having a thin portion 73 acting as a safety valve is welded to one opening 72 in the battery can, and the side of the battery can opposite to the opening 72 is provided with a projecting opening, through which a positive electrode terminal 75 of aluminum, etc. coupled to the power-generating element is led out. While an insulating bush 76 having a hole through its substantially central portion is inserted over the positive electrode terminal 75, the projecting opening is sealed from its sides by means of pressing and crimping, thereby closing up the battery can.
However, problems with the prismatic battery comprising such a positive terminal structure are that 1) the volumetric efficiency of the positive terminal structure is low due to the height of the projecting portion of the positive terminal when the prismatic battery is built in equipment, 2) the positive electrode terminal is sensitive to external force, and 3) it is difficult to maintain stabilized air tightness. Problems 2), and 3) may be solved by a selection of the optimum production conditions or material. However, structural problem 1) with the projecting portion of the positive electrode terminal is difficult to solve.
It is therefore an object of the present invention to provide a prismatic battery which is suitable as a power source for miniature electronic equipment and has high volumetric efficiency, and comprises an electrode terminal portion having high airtightness.